The impact of environment on the comprehension of declarative communication in apes.

A series of recent reports have questioned the ability of great apes to comprehend declarative communication and have suggested that this ability is biologically based and may have driven the evolution of human language. We tested three groups of differently reared chimpanzees and bonobos for their ability to understand declarative signals in an object-choice task. The scores of the two groups of apes that were reared in a sociolinguistically complex environment were significantly higher than the scores of the standard-reared group. The results further showed that bonobos did not outperform chimpanzees. Our results demonstrate that environmental factors, particularly access to a sociolinguistically rich environment, directly influence great apes' ability to comprehend declarative signals and suggest that, contrary to recent claims, apes have the biological capacity to utilize purely informative communication.